1. Field of the Invention
The present invention relates to an optical projection device and the adjusting method thereof. More particularly, the present invention relates to an optical projection device for projecting an image with high brightness and high contrast, and the adjusting method thereof.
2. Description of Related Art
Recently, projectors such as liquid crystal projectors and digital light processing (DLP) projectors are gradually replacing the conventional cathode ray tube (CRT) display, since the conventional CRT display is large and heavy. In contrast, the projector is lighter, thinner and portable, and can be connected to digital products for displaying images. Therefore, manufacturers have developed a variety of inexpensive multi-functional projectors. In addition, the projectors can also be used for presentation at school, company or other public places, even for displaying movies for entertainment at home. Therefore, it is highly desirable to improve the quality of the projectors for improving the display quality of image in order to have a competitiveness edge of the market.
As shown in FIG. 1, the conventional optical projector 100 includes an illumination system 110, a digital micro-mirror device (DMD) 120 and a projection lens 130. The illumination system 110 includes a light source 112, a rod integrator 114, a lens 116 and a reflection sheet 118. The light source 112 provides a light beam 112a, and the rod integrator 114, the lens 116 and the reflection sheet 118 are disposed along the light transmission path of the light beam 112a. The lens 116 is disposed between the rod integrator 114 and the reflection sheet 118. The DMD 120 is disposed behind the reflection sheet 118 along the light transmission path of the light beam 112a. The projection lens 130 is disposed behind the DMD 120 along the light transmission path of the light beam 112a, wherein the projection lens 130 includes a stopper 132.
In the optical projector 100 described above, the light beam 112a provided by the light source 112 sequentially passes through the rod integrator 114, the lens 116 to reach the reflection sheet 118. The reflection sheet 118 reflects the light beam 112a towards the DMD 120. Thereafter, a plurality of micro mirrors constituting the DMD 120, at “ON” state, reflects the light beam 112a towards the projection lens 130. On the contrary, the micro mirrors constituting the DMD 120, at “OFF” state, diverge the light beam 112a from the projection lens 130. Thereafter, the projection lens 130 projects the light beam 112a on the screen 300 to form an image on the screen 300.
In general, since a variety of errors may occur, for example, due the size of light source 112, rod integrator 114, lens 116, reflection sheet 118 and DMD 120 used, the oblique angle of the micro mirrors of DMD 120, the position of stopper 132 of the projection lens 130, and the relative position between various components of the projector. It should be noted that the cumulative error of various errors described above degrade the quality of the image projected by the projector 100, and thereby indirectly decrease the yield of the optical projector 100. Hereinafter, the influence of the oblique angle of the micro mirrors of the DMD 120 and the position error of the lens 116 will be described as an example.
FIG. 2A and FIG. 2B illustrate the relationship between the oblique angle of micro mirrors of the DMD 120 and the imaging position of the image. Referring to FIG. 2A, the oblique angle θ of the micro mirror 122 of the DMD 120 (as shown in FIG. 1) is 12° under normal condition. When the micro mirror 122 is at “ON” state, the light transmission path of the light beam 112a includes path A and path B. At this moment, the light beam 122a is incident on the stopper 132 of the projection lens 130. On the other hand, when the micro mirror 122 is at “OFF” state, the light transmission path of the light beam 112a includes path A and path D, and the angle between path B and path D is 48°.
Now, referring to FIG. 2B, if the oblique angle θ of the micro mirror 122 of DMD 120 is only 11° and when the micro mirror 122 is at “ON” state, the path B′ diverges from the path B, and when the micro mirror 122 is at “OFF” state, the angle between path D′ and path B is only 46°. Because the light beam 112a cannot be precisely incident on the stopper 132 of the projection lens 130, the brightness of the image is reduced. In addition, the angle between path D and path B, which is 48° under normal condition, is reduced to 460 (the angle between path D′ and path B) when the oblique angle of the micro mirror 122 of the DMD 120 is slightly deflected from 12° to 11°. Therefore, when the micro mirror 122 is at “OFF” state, the stray light of the light beam 112a having large diffraction effect can be easily incident into the projection lens 130. Thus, the contrast of the image is also reduced.
Referring to FIG. 1 and FIG. 4A, if the mounting position of the lens 116 is accurate, misalignment of the light beam 112a being incident to the DMD 120 will not occur. On the other hand, referring to FIG. 3 and FIG. 4B, if the mounting position of the lens 116 is diverged from the desired position, misalignment of the light beam 112a being incident to the DMD 120 may occur.
As described above, since a diversion of the lens 116 from the desired mounting position causes misalignment of the light beam 112a being incident to the DMD 120, the horizontal position (Y-axis) or the vertical position (Z-axis) of the rod integrator 114 is generally adjusted to change the direction of the light beam 112a so as to be incident to the DMD 120. Alternatively, the oblique angle of the reflection sheet 118 is adjusted to change the direction of the light transmission path of the light beam 112a so as to be incident to the DMD 120.
However, the two adjusting method described above may only adjust the direction of the light transmission of the light beam 112a so as to be incident to the DMD 120, but can not adjust the angle of the light beam 112a so as to be incident to the projection lens 130. In addition, the errors due to the components described above may also be cumulated, thus the light beam 112a cannot be precisely incident to the stopper 132. Therefore, the conventional optical projector 100 can only project an image without shadow, but cannot project an image with high brightness.